From a production cost point of view it is advantageous to forward the yarn through the texturing machine at as high a speed as possible. This `throughput` speed may be limited by the speed of operation of the moving parts of the apparatus, the process tension and/or the rate at which twist can be inserted into the yarn. Another limiting factor is the length of the yarn heating and cooling zones required to insert sufficient heat into the yarn for it to reach the required processing temperature, and then to cool the yarn sufficiently before its passage through the false twist device. To facilitate the twist run-back from the false twist device to the start of the heating zone, it is desirable to have a straight yarn path through the heating and cooling zones, which leads to very large machines that are ergonomically difficult to operate. A conventional yarn contact heater heats the yarn to the required processing temperature but operates at a temperature below the yarn melting temperature and only slightly above that reached by the yarn at the heater exit. To reduce the machine size problem, it is known to heat the yarn by means of a heater that operates at a temperature higher than the melting temperature of the yarn, but is considerably shorter than the abovementioned conventional heater. One of the problems associated with this process, that is exacerbated by this solution, is that of an upper limitation on the throughput speed of the yarn in the texturing machine due to instability of processing of the long lengths of insufficiently controlled yarn in the heating and cooling zones, a limitation referred to as the surge speed. An arrangement which reduces this problem, but which is not satisfactory for processing certain types and deniers of yarn, is the `bending` of the yarn path between the heating zone and the cooling zone and/or within the cooling zone, for example as shown in U.S. Pat. No. 4,106,274 or U.S. Pat. No. 5,671,519. In these cases the yam path is subject to an abrupt change of direction within the overall length of the heating and cooling zones that is dictated by the machine configuration, and a compromise must be reached between the conflicting requirements of sufficiently high surge speed, satisfactory ergonomics and the satisfactory passage of twist through the heating zone. Any machine configuration chosen will not be satisfactory for all types and deniers of yarn. Another solution is suggested in U.S. Pat. No. 5,438,820, in which the yarn is pushed out of the generally smooth curved path through the cooling zone to give small abrupt changes of direction of the yarn path in this region. However as in the previously mentioned cases, such abrupt changes of direction are likely to inhibit the passage of twist back through the heating zone.